Communication networks are used to transfer information, such as data, voice, text or video information, among communication devices, such as packet telephones, computer terminals, multimedia workstations, and videophones, connected to the networks. A network typically comprises nodes connected to each other, and to communication devices, by various links. Transmitted information may be of any form, but is often formatted into packets or cells.
Packet-switching network architectures, such as networks using Internet Protocol (IP) or asynchronous transfer mode (ATM) protocols, are widely used. In a packet-switched network, data transmissions are typically divided into blocks of data, called packets, for transmission through the network. For a packet to get to its proper destination, the packet must traverse through one or more network switches, routers or intermediate systems. Typically, a packet includes a header, containing source and destination address information, as well as a payload (the actual application data).
When a call is initiated in an Internet Protocol network environment, a call processor performs the required tasks to setup the call and allocate the necessary resources. In such an environment, a congestion management policy is required to ensure that sufficient network resources are available in the network to handle the signaling and control of the call. If the call processor is in an “overload” condition, where the volume of signaling traffic exceeds the capacity of the call processor, the call processor should exercise overload control. If overload is not properly controlled, system throughput can be reduced, and even cause the network to cease operation. In order to effectively control the load, many systems drop the incoming call requests in order to preserve the quality of service for the ongoing calls. However, in a distributed environment, a better policy is to identify an alternate processor that can handle the new call. If such an alternate processor cannot be found, then the new call is dropped.
Currently, many communication systems rely on a distributed call-processing architecture for reliability and scalability reasons. Internet Protocol-based private branch exchange (IP-PBX) switches, for example, distribute the call processing functionality among many servers. Thus, while the initial call processor that receives the call admission request may be in an overload condition, another call processor in the distributed network environment may be available to process the call.
A number of congestion management techniques have been proposed or suggested that determine the availability of an alternate call processor. These congestion management techniques generally rely on periodic polling of the other call processors in the distributed network Typically, each call processor communicates with every other call processor in the distributed network environment to collect statistics for each call processor. The collected statistics help determine the availability of each call processor to perform a specific task in the event of an overload condition. Thus, such polling-based congestion management techniques increase network overhead and potentially contribute to the overload conditions they are attempting to mitigate.
As apparent from the above-described deficiencies with conventional systems for overload control, a need exists for an improved method and apparatus for overload control in a distributed network environment that admits as many calls as possible. A further need exists for an overload control method and apparatus that alleviate congestion and control overload in a distributed call-processing system with minimal overhead and a low processing requirement load by the call processors.